EFRC

Chemistry in the Center for CatalyticHydrocarbon Functionalization:Fundamental Studies Relevant to Catalystsfor C-H Functionalization

EFRC

Scripps Energy and Materials Center

CH4CH4

H2OH2O

N2N2

CO2CO2

O2O2

EnergyEnergy

FertilizerFertilizerCommodityChemicalsCommodityChemicals

FuelsFuels

Energy SecurityEnergy Security

SustainabilitySustainability

EFRC

Team

Gunnoe/UVA

Vedernikov/UM

Periana/TSRI

Groves/Princeton

Trewyn/Ames

Ess/BYU

Goddard/Caltech Cundari/UNT

Crabtree/Yale

Meyer/UNC

Homogeneous catalysis and organometallic chemistry

Electrochemistry and electrocatalysis

Bioinorganic chemistry and enzymatic chemistry

Computational chemistry and quantum mechanics

Materials chemistry (nanomaterials, electrodes surfaces, etc.)

Natural Gas(CH4)

Electricity

Natural gas

CO2

Materials

Fuels

An Economy Based on Natural Gas

Natural gas

CO2

CH + ½ O2 COH

Next GenerationCatalysts

Why natural gas?

EFRC

Extensive Natural Gas Reserves5

Energy Facts 2011 5

• Stranded gas is a shorter term, less demanding opportunity

• Gas could be at zero or negative cost

• Smaller, less expensive portable GTL units could process smaller NG reserves

• Less demanding requirements could accelerate implementation 

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Flared Gas is an Immediate Need

• Gas at negative value• Require small Inexpensive GTL Units

• ~25% of US needs is flared

• Current high Temperature, syngas technology too expensive and complex for these applications

EFRC

CH4

Electricity

Natural gas

CO2

Materials

Fuels

Implementing the Natural Gas Economy

Natural gas

CO2

CH3OH The future

IntermediateFeedstock

Technologies known or in development

Why Methanol (DME)?

EFRC

Current technology to convert CH4 to Liquids  

70% yield! 

Mature technology!

Practiced at fuel scale!

Uses only AIR as the co‐reagent!

~25%900oC

MeOH

NaturalGas

Air

Synthesis Gas (CO/H2)

~60% MeOH

Fuels

Chemicals, CO, H2

Power

Fischer–Tropsch

Key to cost reduction is lower capital cost!

8

Selectivity of any new process must be >~80 – 90%!

EFRC

Technology Needed

NaturalGas

AirMeOH

Direct, Selective,Lower Temperature Methane  Oxidation

Fuels

Chemicals

Power

CH4 + ½ O2 CH3OH

250 oC

Goal:  >50% reduction in costrelative to existing technology

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The ChallengeSlide 10

of 69

H3C-H + ½ O2 H-CH2-OH CO2 + H2O

Utilize catalyst to  activate (increase reactivity) of RH

Utilize catalyst to  activate (increase reactivity) of O2

MinimizeEFRC

High Selectivity by Minimizing Product Oxidation

RH gas

RH lig ROHlig ROPlig

CO2 gas CO2 gas

Kp

k2

k1

k3P

Poor selectivity without “protection” since k2 > k1

High selectivity with “protection” if Kp >> 1 and k1 >> k3 << k2

P group needs to be inexpensive, stable and easily recycled

11

The strategy capitalize on reactivity of OH groupProduct protection strategy

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Commercial Wacker Process for Partial Oxidation of Ethylene

C2H4 + Ox+ H2O   CH3CHO +  H2Ox C2H4 + Ox+ H2O   CH3CHO +  H2Ox  H2Ox + ½ O2 Ox  + H2OH2Ox + ½ O2 Ox  + H2O

Ox = 2Cu2+Ox = 2Cu2+Pd2+

Homogeneous catalysis

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Wacker Process Design can be Utilized for Partial Oxidation of CH4

CH4 + ½ O2 CH3OH

H2Ox + ½ O2 Ox  + H2OH2Ox + ½ O2 Ox  + H2O

13

CH4 + Ox+ H2O   CH3OH  +  H2Ox CH4 + Ox+ H2O   CH3OH  +  H2Ox 

• Selective Partial oxidation• Lower capital and operating costs• Lower temperature• Gas/Liquid system• No air separation• Inherently safer• Easily scalable

• PdII is not effective

• New homogeneous (molecular) catalyst design 

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Minimum Metrics for Measure Success

Key engineering guidelines >90% Product Selectivity >20% Methane conversion per pass Temperature >200oC but < 300oC Reactor volumetric productivity (STY) ~10‐6 mol/cc.sec Inexpensive product separation

Key Catalyst Guidelines TOF ~1 s‐1

TON >103 

Can molecular catalysts meet these targets??

EFRC

Metrics to Measure Success

Engineering Guidelines Avoid explosive mixtures >20% Methane conversion per pass >90% Product Selectivity >20% Oxidant conversion per pass Non‐corrosive materials for inexpensive reactor construction Facile product isolation Pressure <500 psig Temperature >200oC but < 300oC Reactor volumetric productivity (STY) ~10‐6 mol/cc.sec  = [cat] x TOF

Key Catalyst Guidelines TOF ~1 s‐1 TON >103  Catalyst concentration of 1 mM at TOF = 1 s‐1 to be cost effective At 1:1 gas:liquid should generate 2M MeOH in ~1.5 hr 

Periana, J. Mol. Cat., 2004, 22, 7

Molecular Catalyst Design

The ChallengeSlide 17

of 69

H3C-H + ½ O2 H-CH2-OH CO2 + H2O

Utilize catalyst to  activate (increase reactivity) of RH

Utilize catalyst to  activate (increase reactivity) of RH

Need to minimize

Basis for Focus on Molecular Catalysts

Well Defined

Full Molecular Model

Poor  Catalyst Separation

Very Selective

Fast below 250oC

Full synthetic Control

“Rational” Design 

Inexpensive Heat Transfer

Gas‐Liquid or Gas‐Solid

Inexpensive Reactors

Low Operating Costs

Unstable above 250oC 

Emerging

TSRI Confidential

Expensive EFRC

EFRC

CatalystDesign

QuantumChemistry

CatalystTesting

RapidScreening

Molecularcatalysts

Can Integrate Modern Tools to Reduce time to Market

PredictiveModel

Mechanisticstudies

Approaches to Catalyst Design20

CH4 +  ½ O2 CH3OH

LnMX

[LnMO]+

½ O2

CH4+ X‐

CH3OH

½ O2+ HX

LnMX

LnM‐CH3

HX

CH4 CH3OH

Activatedintermediate Activated

intermediate

X‐

CH4 NOT “INVOLVED”O2 NOT “INVOLVED”

O2 ActivationCH Activation

Avoid free radicals

EFRC

LMX Catalysts Identified by “Theoretical Chemistry”

(In + Hsolv) / n

z/r (Å)

H+

Fe3+

Cr3+

La3+

Co3+Mn3+

Cu2+

Sn2+

Cr2+

Rh3+

Ni2+

Tl3+

Au1/3+Pt2+

Cd2+ Pb2/4+

Hg2+

Pd2+

Ag+Cu+

In+

Ti4+

I+Xe2+

Borderline RedoxElectrophiles

Hard RedoxElectrophiles

Bi3/5+Ir+

Rh+

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Several Effective Electrophilic Catalysts Operate by Electrophilic CH Activation

STY ~ 10‐7 mol/cc.sec

~1M methanol

Stable

>90% Selectivity

~80% methane conversion

All Catalysts operate by CH Activation

N N

N NPt

Cl

Cl

Science, 1998

Hg(II)/H2SO4

Science, 1993

I+/H2SO4

Chem Commun2002

Pd(II)/H2SO4

Science, 2003

Au(III)/H2SeO4

Angew Chem. E.2004

Cat220oC, 2.5 hrs

150 ml 98% H2SO4500 psig ~ 1M

CH4 + H2SO4CH3OH + H2O + SO2

22

Acid solvent is essential!!

Soft, Redox active electrophilesEFRC

EFRC

Catalysts inhibited by Products in Strong Acid Solvents

6 7 8 9 10 250

0.5

1.5

2.0

2.5

100

3.0

H+

(1960)

Hg2+

Fuels?

Chemicals?

Ho of D2SO4 solvent

K x 10

4s‐1

Need second generation catalysts!

N N

N NPt

Cl

Cl

Cost comparable to existing MeOH.  Not applicable to large fields

Stranded gas?

CATA

LYST RAT

E

10‐3

Process Economics Show that this is not applicable to Large Fields24

Vent

Methanol

Nitrogen

Air

Natural Gas

H2O/SO2

H2SO4

Mechanistic Studies Show that Systems Operate by CH Activation

CH4

H2SO4

CH Activation

SO2 + 2 H2O3 H2SO4

H2O

N N

HN NPt

X

CH3

X

Cl

X = HSO4

+

N N

N NPt

Cl

Cl

CH3OH

Sol2+

2 X-sol

N N

HN NPt

Cl

[Sol]

- HCl

Sol = H2SO4

X-sol

1/2 O2 H2O

Pt[Sol]CH3

+

X-sol

N N

HN N

N N

HN NPt

[Sol]CH3

X

Cl +

HX

[CH3OH2]+

o]RH[TOF HHN N

NNPt

Cl

CH3

H

+2

1.55 1.73

2.17

25

EFRC

Current Proposed Reaction Mechanism

28 kcal/mol

Coordination is Rate determining

H2SO4 facilitatescoordination and cleavage

26

EFRC

Several Possible Mechanisms:  A, B, C and D27

N

N

HN

N

XPtIV

CH3

X

X

+

X-

N

N

HN

N

XPtII

CH3

+

X-

N

N

HN

N

XPtII

X

+

X-

1

2

3

N

N

HN

N

XPtIV

X

X

X

+

X-

4

CH4

HX k6

k-6

k5

H2SO4 + 2 HXSO2 + 2 H2O

k2

CH3X + HX

k3

H2SO4 + 2 HX

SO2 + 2 H2Ok4k-4

k1k-1

CH4

HX

X = Cl-, HO3SO-

Original mechanism, A,Is wrong.  Reactions proceeds by pathway D.

Can we get 103 increase?

27

EFRC

New Catalyst Designs

N

NN

N Pt

Cl

N

N

NN

N Ir

ClCl

Cl

RhO O

OOL

ORh

O

R

L

PtO O

OO

L

+

OsO O

OOL

L

N

N Ir

XX

X

OPt

N

TFA

TFA

O

N N

N NIr

OH2

Cl

IrO O

OO

CH3

N

N NPt

OH2

Cl

Rates too low

Very stable

28

EFRC

Approaches to Catalyst Design29

CH4 +  ½ O2 CH3OH

LnMX

[LnMO]+

½ O2

CH4+ X‐

CH3OH

½ O2+ HX

LnMX

LnM‐CH3

HX

CH4 CH3OH

Activatedintermediate Activated

intermediate

X‐

CH4 NOT “INVOLVED”O2 NOT “INVOLVED”

O2 ActivationCH Activation

Avoid free radicals

29

EFRC

Ni-CoM-dependent Methanogenesis

S. W. Ragsdale and C. WilmottJ. Am. Chem. Soc. 2011, 133, 5626

30

EFRC

MNN N

N

O

L

HCH3

MNN N

N

O

L

H CH3

MNN N

N

O

L

H HCH3

MNN N

NL

CH3

H2O

HO

MNN N

NL

HO-CH3

Strategies for the oxygenation of strong C-H bonds

MNN N

CH3

O

L

HCH3

MNN N

O

L

H

H3C-CH3

HO-CH3

MNN N

O

L

H

OCH3

H2OH+

?

31

EFRC

Methane Activation by Rhodium Porphyrins

Wayland B. JACS, 1990;  DiMagno, S. G. J. Am. Chem. Soc. 2000; Han, Y. Z.; Sanford, M. S.; England, M. D.; Groves, J. T. Chem. Comm. 2006, 549‐551; Sanford, M.S.; Groves, J.T. Angew. Chemie 2004, 116, 598‐600. 

32

EFRC

Several Effective Electrophilic Catalysts Operate by Electrophilic CH Activation

STY ~ 10‐7 mol/cc.sec

~1M methanol

Stable

>90% Selectivity

~80% methane conversion

All catalysts operate by CH Activation

N N

N NPt

Cl

Cl

Science, 1998

Hg(II)/H2SO4

Science, 1993

I+/H2SO4

Chem Commun2002

Pd(II)/H2SO4

Science, 2003

Au(III)/H2SeO4

Angew Chem. E.2004

Cat220oC, 2.5 hrs

150 ml 98% H2SO4500 psig ~ 1M

CH4 + H2SO4CH3OH + H2O + SO2

33

Applicable to flared gas? EFRC

Summary and Future Directions34

Molecular catalysts that operate in solution at lower temperature by CH activation has been shown to be effective and potential practical for conversion of methane to methanol 

High selectivity observed in these systems can be attributed to fast reaction at lower temperatures and reaction without the involvement of free‐radicals, and reversible protection 

Issues such as cost, stability, separations, etc. can be addressed through catalyst modifications, changes in solvents, oxidants, etc.

A key basis for effectiveness of molecular catalysts is that detailed atomistic models can be obtained that together with a wide variety of synthetic tools utilized to “rationally” design improved catalysts.

An important focus is increasing catalyst rate by ~103

To speed up discovery, the iterative loop of synthesis, characterization, testing and study must be accelerated

An important strategy to accelerating progress while minimizing risk  is to leverage efforts directed at the other small molecules, O2 ,N2, CO2 and H2O

EFRC